1. Field of the Invention
The present invention relates to a zoom lens and an image pickup apparatus equipped with the same.
2. Description of the Related Art
In recent years, digital cameras that pick up an image of an object using an image pickup element such as a CCD or CMOD sensor have replaced film cameras to become the mainstream.
Among such digital cameras, cameras of a type that is small in the dimension with respect to the thickness direction (i.e. direction along the optical axis) to facilitate portability have been favored.
On the other hand, although the zoom ratios of zoom lenses used in compact digital cameras are typically about three, zoom lenses having higher zoom ratios are demanded recently.
There is a known type of zoom lens that can easily achieve a high zoom ratio, that is, a zoom lens having three or more lens units including, in order from the object side thereof, a first lens unit having a positive refracting power, a second lens unit having a negative refracting power and a rear group having a positive refracting power, the lens unit located closest to the object side in the rear group being a third lens unit having a positive refracting power.
For example, Japanese Patent Application Laid-Open Nos. 2005-242116, 2005-326743 and 2006-78979 disclose zoom lenses having a zoom ratio of about 4.5.
In these zoom lenses, in order to facilitate magnification change provided by the second and the third lens units, the first lens unit and the third lens unit are moved in such a way as to be located closer to the object side at the telephoto end than at the wide angle end, and the second lens unit is fixed or moved in such a way as to be located closer to the image side at the telephoto end than at the wide angle end.